Gas analyzer and method of use



y 1953 w. M. zAlKpwsKY 7 GAS ANALYZER AND METHOD OF-USE Original FiledMarch l, 1943 GAL FUEL AlR RATIO INVENIT.OR. WLADIMIR M. ZAIKOWSKY ATTORNE Y GALVANOMETER DEF LEGTION associated with a common passage 95.The other two test cells 99 and 9| are positioned in the other two armsof the bridge and are associated with a common passage 96. The outputends of these two passages and 96 are connected together at a junction97 and through a valve 98 to an exhaust pump 99, which may be drivenfrom the engine 54.

The valve 98 normally connects the junction 91 to the pump 99, but, whenturned counterclockwise 90, admits atmospheric air through aconstriction 98a to the junction 91 for a purpose to be later described.I

The two passages 95 and 96, respectively, are supplied with exhaust gasfrom the exhaust manifold preferably through a common constriction I00,but through two separate treating tubes IN and I02, respectively. It maybe assumed that the treating tube IOI contains carbon and that thetreating tube I02 contains copper oxide. Both treating tubes are shownpositioned within the exhaust manifold 60 so that they will be heated tosuitable reacting temperatures by the exhaust gases, but the heatingcould be done in a separate furnace. The outlet of the treating tube INis permanently connected to the passage 95 but a valve I03 is providedbetween the treating tube I02 and the passage 96. In its normalposition, this valve functions only to admit gas from the tube I02 tothe passage 95. When the valve I03 is turned counter-clockwise throughan angle of 45 as shown in Fig. 2, a passage I04 in the valve connectsthe passage 96 through a conduit I05 with the passage 95 so that gaspassing through the treating tube IN is admitted to both the passages 95and 96; and a passage I09 in the valve admits air through a needle valveI03I into the outlet end of the treating tube I02.

The single meter 85 is employed both to indicate the condition ofbalance of the bridge and the current flowing through the bridge. Whenthe switch 86 is thrown into its upper position, the meter is connectedacross the bridge. When the switch is thrown to its lower position, themeter is connected in shunt to a resistor I II permanently connected inseries with the variable resistor 94 and the battery 93. The resistorIII is provided to decrease the sensitivity of the meter 85 when it isconnected to show the current flowing through the bridge, because thetotal current delivered to the bridge is enormously great as compared tothe current that flows through the meter in response to unbalance of thebridge when the switch 86 is in its upper position.

The apparatus of Fig. 1 is operated as follows: First the switch 86 isthrown into lower position and the total current flowing in the bridgeis adjusted by resistor 94 until the meter 85 indicates a predeterminedvalue for which the system has been calibrated. The switch 86 is thenrestored to its upper position. Then the valve I 03 is swungcounter-clockwise to admit the same gas from the treating tube IOIthrough both test channels 95 and 96, and the bridge is balancedbyadjusting the potentiometer 92 until the meter shows zero current. Thisparticular meter is in neutral position, both mechanically andelectrically, and indicates zero current, when the hand is at 0."Finally, the valve I03 is restored to its normal position, as shown inFig. 1. Thereafter, exhaust gas treated with hot carbon in the tube IOIpasses through the passage 95, and exhaust gas treated by the hot copperoxide in tube I02 passes through passage 96. These two diiferentlytreated gases will have the same thermal-conductivity if the mixture istheoretically correct, but will vary from equality in one direction ifthe mixture becomes too rich and in the other direction if it becomestoo lean, so that the meter will automatically give a direct indicationof the quality of the mixture.

The reason for this will be explained with reference to Fig. 3, in whicha solid curve I I2--I I20 and a dash curve II3-I I3c show the variationsin thermal-conductivities of the untreated exhausts of two fuel-airmixtures, in which the fuel is octane and benzol, respectively. Thesecurves show that a meter calibrated to indicate a minimumthermal-conductivity with one fuel might be grossly inaccurate with adifferent fuel if precautions are not taken in accordance with theprinciples of the present invention as explained below.

Considering now the eifect on the thermalconductivity of the exhaustoftreating it with heated copper. oxide, the left part H2 or II3 of thecurve remains unchanged because there is nothing to oxidize in a lean'mixture. On the other hand, the right part II2c or H30 is drasticallyaltered, because the unburned fuel gases in the exhaust of a richmixture have a higher thermal-conductivity than do their products ofcombustion. Actually, the right (rich) portions of thethermal-conductivity curves for exhaust gas treated with copper oxide(the gas in passage of Fig. 1) are substantially straight extensions ofthe left portions, as indicated at I I2a and I I9a in Fig. 3. Thus curveII2-I I2a represents the variation of the thermal-conductivity of thegas supplied to passage 95 when the exhaust gas from octane is treatedin tube I02. Also curve II3-I I3a represents the variation of thethermal-conductivity of the gas supplied to passage 96 when the exhaustgas from benzol is treated in tube I02.

In the preparationof the curves of Fig. 3 it has been assumed that incontinuous operation, the copper oxide tube may contain enough reducedcopper to absorb the oxygen in the lean mixture.

Considering next the effect on the thermalconductivity of the exhaustoftreating it with hot carbon, the right part I.|'2c or II 30 of the curveremains unchanged because there is no oxygen to combine with the carbonin a rich mixture. The left part H2 or II3 of the curve is altered,because the excess oxygen in a lean mixture has a higherthermal-conductivity than do the products of combustion of the carbon.Hence, the exhaust of a lean mixture, which normally has athermal-conductivity indicated by the curve H2 or I I3, will have athermal-conductivity indicated by the curve II2b or IIlb after treatmentwith hot carbon. Thus curve II2bI I2c represents the variation of thethermal-conductivity of the gas supplied to passage 95 when the exhaustgas from octane is treated in tube I 0| Also curve I I3b-I H30represents the variation of the thermal-conductivity of the gas suppliedto passage 95 when the exhaust gas from benzol is treated in tube I0'IIt is to be understood that under certain conditions of engineoperation, oxides of nitrogen may be present in the exhaust, as well asoxygen, and they are capable of reaction with heated carbon.. It may bedesirable when the amount of nitrogen oxides is appreciable, todecompose or absorb them in a separate treating tube, but it is notordinarily necessary.

. It will be apparent thatin the system of Fig. 1,

'atesams one samplemn treatediexhaustthawina;theithere maleconductivitycharactenistic "shown; ithe curve slim-412w on; LiSi- -T I I 3M1'ciimnaredxwith a: secondisampleio .rtreatedtexhausta havinatthethermalsconductivitttfcharacteristicrshownhy:the curve limbs-4112c or:lLfib-Jilfim. It; v vstill. be om served;- that thentwo; samples;compared have; the same.:- thermaleconductiwityki at," the theoreticalvratio} irrespectivemjoiixthe fuel} ve1ilulixvndii sincetheyiintersectaatithatpoint;i

2In z-Eig; Eitheauppertcurvessrepresentsvariations inthermalecondiictivity :that,.:wcu1d;. obtained if thegexhaust samplesidentified:therewithtwere competed: against:al-fixedirefeizence gas;such; as air, but.- they de'e riots necessarilyrtrepresenti the exactgalvanometer v:readingaaand}. their/vertical position-the:- graphiwithrespect; to. themverze tiicalipositionotthefv Iowenicurwes: :and: M5; no1 significance.- "Irre'spectivoe ioflthi's'; .rwh'endthe two:samplesctreatcd; withfihobicarbon) and i" with copper, oxide.rr'espect-ively; vare; compan'ednwith each oither in: the: system; fFigs 1:, that-actual ga'lvanometer readings correspond: torthe'dinesentialsiofithe upperzcuryes; andl'theiresultantzdifs ferentia-lwcurve elitist; represent'sstha galizanometmreadings actually obtainedfor diiiierenti fueii-air'. ratios when .benzoli is the duel; .anda the:& curve iii 5: represents actual: galvanomete readingsmhtainedxforr,different,-fueleair'snatios JhBh the; fuel is! octane.These-tenures: M4: and; ldtkhaveisev=- erals interesting;characteristics(1) They both pass through zero at theatheo retically perfect mixture.Hence, if the system is calibratedhto showizero: reading on meter 815inFig. '1, fortheoretically" perfect' ratio of one fuel, it iscalibrated to shbwa-zero-reading with the theoretical. ratio ofany-iuel;Furthermore, the bridge 81can'be balancedmfor: zero current attheoretically perfect mixture; so that the m1 maliposition of rest (of:th'eimeterhand is .at zero, and. variations. in thefi'current. in thebridge, produced by varying the re'sistorSAior the-purpose of varyingthe sensitivity, can be made without: shifting thehandl-away from zeroposition. In actual practice, the balance .ofthe bridgecan be .qui'ckly'testeda-atany timeby simply throwing the valve 103 into the positionshown in Fig. 2 :to admit ithei same gas from the treating tube I intoboth of" .the' passages 95 and 95.

0291 The curves tim andl l 5: vary in opposite directions for lean" and.rich mixtures; respectively, so that the meter handr -movesll-in onedirection away from the zeronpoint to indicate lean mixtures, and" inthe opposite direction away from the zeropoint 'td indicaterichmixturesr This eliminatesallthe disadvantages of attempting to.determine: the minimum thermalconductivityof thegas.

('3) The twocurves-114 iand l'i fi differ from each other onlyslightlylat' any part ofthei'r range and differ scarcely at 'all 'closeiy adjacent the zero point. This makes it possible to ad'- just thebridgeto the- .same sensitivity' ior all fuels and eliminates the necessity'of-separately calibrating: it i f or each particular-"fuel that may beem'ployed.

(4) The slopes of the ourves for lea-n mist tures, although less thanthe slopes; for rich mixtures, are appreciably greater than the-slopesof the curves I i-2 I l-2b; t /aridlithithereby giving superiorsensitivity in lean range as compared withitha't obtainable 'piiiozltnowh arrangements.

Ithas previously been indicated that the oper- 75* atorrcanz check the:balances ofzithesbr-idgei-in the system. of? Fig: 1&- atzanm timeubwthrowinguthe valve lfl3'.:-vinto; -thei position:shownv ins fiEigazt toadmit: the same: gas cfromzttheiztreatingir tube 1.01 into both of thepassages and 96. Thisvalve is' so'sarranged asztoiperformanotherzusefulifunction. Thus; airsi'ss by -passedthroughhithexneedlevalve 1.031 anch'theivalve; passage 1133 through the copper:oxideiatuheaiflsi vin: reverserdirection, then through the conduit. ilaUJz, i w: the: exhaust pump 99? This; circulation of; atmospheric";air over the hot copperzoxidezin theitnhe; lfi ziregem crates: it: byreoxidizing; reducedicoppen:backz'to copperzoxi'de. Airientermthepassageiiflii through the: valve lfli'i'i as: shown, .torlimit thepressure and" prevent: sa ire-from; also flowing throughthe tube 1 n land, consuming; theccarbon. :Such'v'fiow of HiI'..;f1'.0i1 tube.lulr'tostube Hill can .aisozihe prevented. by pros/idling; separate.constrictions for tubes llll ande L322; instead; on: supplying; thembothzfromythe singleconstrictiom m;t=..

Theasuction- :pumpt 9-91 is; pr.ef eraio1y'.:,oi2 such capacity:relative; i110.-'bh8' constriction liim asato maintain, a low:pressurezin. that gas passage; and cells;

One: great, advantageaofi low: pressure-1 opera-.- tion in the system ofFigiia is: thee reduction of the; lag; between? a; change: in;composition: of? the mixture. and. anuindicationzthereof byztheuinestrument; hutzanothenwery important: advantage ofz thelowpressureaoperationtis ithe. reduction in the: rate: of; consumption of::thezcarhoxr.andiethe copper .oxide in the: treating: tubesil M4,andioliizi As; a matter: of fact; the. reduction: in; the-press suresometimes/makes itz feasihle; tio .empleyza systemutilizing...thesereagentsewhere: itvwould be utterly impracticable ins?operationat normal atmospheriepressures.

.I find that; isisufficientc andenen. preferable tohe'aticoppersoxi'dezto at relatively lowrtempe zae tune; from 3,00?.'(C.)I tm4009 at which. only complete combustioni of; hydrogen-andcarbon monoxide is assured, while methane remains.

unaffected; known, for: complete combustion: of methane copper. oxideshould be heated "tow a temperature of: 7-00?- (.G.) on. more; However,.theametho'dicanloe ipxacticedz withivtery wide: range of 1temperatures;

Asdong as the pumbtfliismunning, :theexh'aust gases:v insthe system:remain. expanded; and; the

' dewtpoint of tatheegases is: suificiently low; to {prevent anycondensation; of i watch: withinthemsyst'em. However-,; .whenmthe.pumpjsostopped-e-if exhaust gasicontinued-"to flow-i throughithe-restrictioni10.0; untilthe systemwas rfllied atiatmospheriespressure-the watersvapor pressuresmighturise above the dewpointywith.resultantrprecipitation. It is important toiprevent'isuchcondensationsincethe watenmightvremain for an indefinite period ortimenin lthetcells and cause damageztoi-the insular tionby. corrosion.There; are waysponprenenting such condensation, :oneot whi'chiis todrive the suctionupumptfli fromrthe engine; the exhaustof whichisahemgianalyzed, sosthatitheqpump oon tinues; to operate as longlasazthet .fueleiiow ta -the engine-is continued. Whenithe.,engineiis'istepped', either by cutting the ignition or shutting oiithe. fuelifiow, the 'engine-normally will: continue tokrotatertbyritsumomentum long; enoughito scavenge fromwthe eXhaustmaziifoldexhaust-productshigh inuwat'er content, so that, =by'the time the-engineandnpump stop, the exhaustlmanifold fifl 'willbe filiedew-ith air ;orsain'efuei mixture containingso' atmospheric humidity. Therefore, thelast: periodicit operation relativeiy drp .aiii w il'ls-fiow 7 throughthe passages 95 and 96, while the pressure in those passages and in thecells is rising to atmospheric pressure, and condensation of water inthe cells and passages will be effectively prevented.

In those instances in which the suction pump 99 is not directly coupledto the engine 54, the valve 98 may be employed to prevent condensationof liquids in the apparatus by rotating this valve counter-clockwise 90shortly before or simultaneously with the shut-down of the pump 99. Thisadmits atmospheric air through the constriction 98a to the junction 91,and thence back up into the passages 95 and 96, filling those passagesand the cells associated therewith with atmospheric air at atmosphericpressure. The constriction 98a prevents a too rapid inrush of air intothe cells. It is possible for the filaments in the cells to be damagedby sudden admission of gas thereto at full atmospheric pressure.

The constriction I serves as very effective means for preventing damageto the filaments (resistors) in the test cells from explosion in theexhaust manifold, which occasionally happen. Elimination of this dangermakes it possible to use larger diffusion passages in the cells thanwould otherwise be safe.

Thermal-conductivity cells of the general type employed in the systemsofar described are well known, and many of the cells already in use canbe adapted for operation in my system. However, I have developed aconstruction of cell that has special advantages, and which is disclosedin my corresponding application, Ser. No. 582,467, filed March 13, 1945to which reference is made.

It is apparent from Fig. 3 that a given departure from theoretical ratioon the rich side produces a much greater change in thermalconductivitythan the same departure on the lean side. It is desirable, therefore, touse a meter having an asymmetric scale in which the "lean range isshorter than the rich range, as shown in Fig. 1.

It is possible to obtain deflection of an indicating meter to one sideof a 0 or neutral point to indicate lean mixtures and to the other sideto indicate rich mixtures by comparing treated exhaust gas against air,and a system utilizing this mode of operation is illustrated in theschematic diagram of Fig. 4, which shows a portion of the exhaust andintake system of Fig. l in combination with a single bridge having areference cell 16 exposed to air from the intake pipe 62 and a test cell11 which may be supplied through a valve 18 either with untreated ortreated exhaust gas from the exhaust manifold 60. When the valve is inthe position shown, untreated exhaust gas, after being expanded bypassage through the constriction 19, is conveyed directly past the testcell 11 and thence to the exhaust pump 80. However, if the valve 18 isrotated 90 clockwise, then gas can no longer pass directly from theconstriction 19 to the'test cell but must flow through a tube 8|positioned within the exhaust manifold 60 for heating purposes andthence through the valve 18 to the test cell 11.

The apparatus of Fig. 4 is operated as follows: First, with the currentadjusted to the value for which the meter scale is calibrated, the valve18 is positioned as shownin the drawing so that untreated exhaust gas isdelivered to the cell 11, and the carburetor 51 is adjusted until themeter 65 indicates minimum thermal-conductivity- Then the bridge-isadjusted by manipulation of the potentiometer 62 to bring the hand ofthe meter to the 0 point on the scale, indicating theoretical mixture.Thereafter, the valve 16 is rotated clockwise, causing exhaust gas topass through the treating tube 8| and thence to the cell 11. Thetreating tube 8| may contain an oxidizing agent such as copper oxide, orit may contain a reducing agent, such as solid carbon. If an oxidizingagent is employed, then all unburned fuel in the exhaust is oxidized andthe thermal-conductivity of the gas reaching the cell 11, instead ofhaving the characteristic shown by curves H2 and I He in Fig. 3,gradually and continuously decreases in thermal-conductivity as the rmixture becomes richenas shown by curves H2 and 2a. On the other hand,if the tube 6| contains a reducing agent such as carbon, then all excessoxygen in the exhaust is burned to carbon dioxide and the resultant gasreaching the cell 11 will have a, continuously lower thermalconductivityas the mixture varies from rich to lean, as shown'by curves 2c and HZb.In either event, the scale of the meter 65 can be calibrated so that thehand will indicate directly whether the mixture is theoreticallycorrect, too lean, or too rich.

To properly explain the invention, several embodiments thereof have beendescribed in detail, but it is to be understood that the invention isnot limited to the particular embodiments shown, but only to the extentset forth in the appended claims.

I claim:

1. In a method of determining the ratio of a fuel and air mixture beingsupplied to a combustion device, the steps which comprise: forming afirst stream of exhaust gas exhausted from said device; treating saidfirst stream of exhaust gas with an oxidizing agent which will alter thethermal-conductivity of such exhaust gas only if said mixture is rich,the thermal-conductivity of said first stream thereby decreasing withthe fuel-air ratio; forming a second stream of exhaust gas exhaustedfrom said device; treating said second stream of exhaust gas with areducing agent to alter the thermal-conductivity oi such exhaust gasonly if said mixture is lean,

the thermal-conductivity of said second stream thereby increasing withthe fuel-air ratio; and comparing the thermal-conductivities of said twotreated streams; whereby theoretical ratio is indicated by equalthermal-conductivities of the streams, a lean mixture is indicated by adeparture from equality in one direction, and a rich mixture isindicated by a departure from equality in the other direction,independently of variations in the absolute thermal-conductivities ofthe exhaust gas resulting from different fuels.

2. In a method of determining the ratio of a fuel and air mixture beingsupplied to a combustion device, the steps which comprise: forming afirst stream of exhaust gas exhausted from said device; treating saidfirst stream of exhaust gas with hot copper oxide to alter thethermalconductivity of such exhaust gas only if said mixture is rich,the stream thereby decreasing with the fue1-air ratio; forming a secondstream of exhaust gas exhausted from said device; treating said secondstream of exhaust gas with hot carbon to alter the thermal-conductivityof such exhaust gasv only if said mixture is lean, the thermalconductivity of said second stream thereby increasing with the fuel-airratio; and comparing the:

thermal-conductivities of said two treated thermal-conductivity of saidfirst qiial jifidica df byg-a"departuretwin-equality in; theotherdirection;findependentl the absolute thermal-child 'liaustgas'rc'sul-tingjironr differentfuels,

3 Thermal-conductivity exhaust a s analyz ing ppa'ratusj comprising;ap'air of; test cellsga metering "s stem rcr -iridicatingflthe magnitudeand-direction or departure nometiuality "of the thel'inal conductivitiesof the 'gases in -said tn-'0 cells separat'econduits *for delivering'two streams of the exhau'st g'as t6 be' tested to said-respectivecells; oneof said mmense-macaw; a charge ofa-solid xidizi'n'g"agent-adapted to" oxidise umou -heave r cemponen'ts in tlie streambeing delivered to one of saidfcclls; and the -othe1"condii'it"including a'charge cf a solid reducing agent aid'apte'd to '(zornbinewith free oxygen in the stream 'bein' delivered to the o'thel"said-cell, whereby theoretical mus is indicated by equal thelirrialconductivi ties oi -the 'streams, a lean mixture is indicatedby adeparture from equality r f t fl b e r r mm ant n $119 in oned'irection; and a rich mixtures indicated by a departureffrom equality:initheother direction, independent of variations in the absolute thermalconductivities of "the exhaust gas r esiilb ingi from'Idi'ffer'ent'fuels.

4;- niermai-coneu'cuvii can (at gas analyzing apparatuscomprising: a'pan'oi test cells, a

metering; systemfor/ indicating the magnitude and; direction of. 1departure from equality,- of v -the thermal -conductivities 012 the:-',g cell's, separate conduits ior idelivering two streams of theexhaust gas to be tested to said respective cells, one of said conduitsincluding a charge uses "111? said: two

of copper oxide adapted to oxidize unburned fuel components in thestream being delivered to one of said cells, and the other conduitincluding a charge of carbon adapted to combine with free oxygen in thestream being delivered to the other said cell, whereby theoretical ratiois indicated by equal thermal-conductivities of the streams, a leanmixture is indicated by a departure from equality in one direction, anda rich mixture is indicated by a departure from equality in the otherdirection, independent of variations in the absolutethermal-conductivities of the exhaust gas resulting from differentfuels.

5. The method of analyzing exhaust gas resulting from combustion of afuel containing car com with air which comprises: producing two streamsof said exhaust gas; treating one of said streams with a solid oxidizingagent so as to complete oxidation of substantially all carbon in saidone stream to carbon dioxide; treating the other stream of said exhaustgas with a solid reducing agent so as to consume substantially all freeoxygen in said other stream; and measuring the difference in thethermal-conductivity of treated portions of said two streams.

6. The method of analyzing exhaust gas resulting from combustion of afuel containing carbon with air which comprises: producing two streamsof said exhaust gas; treating one of said streams with hot copper oxideso as to complete oxidation of substantially all carbon in said onestream to carbon dioxide; treating the other stream of said exhaust gaswith hot carbon so as to consume substantially all. free oxygen in saidother stream; and measuring the difference in the thermal-conductivityof treated portions of said two streams.

1 1 7, 'paratus" for, analyzing jtheigasflowin g,

, H haiis't, Lcondiiitt connected to a ."device in which 'itlie"ebmbustmn prise. a hydrocarbon ,fiielioccurs and which produces hotexhaustl'gases i coihpr 'ing,. 'a. mainl exhaust. conduit. connected Iai'd fdevicefi for ile'adingloff hot exhaust ,ga ses t fere'fronn a,pair of test 01 115,, separate 3 branch "cqn'duits foriilowing streamsofexhaust gas I from 1 'sai 'mainlexhaustfconduitoto said respectivecells, l v

portio s .ct vthe respective. branch conduits/(being located in heatexchange relationship with heated exhaust. gas liiowing in. Said, mainexhaust con duit, a charge,offa salidfoxidizingagent adapted til, 0"idize unburned.IueLcOmpQnents located .in the-"heated. lportiono'f. one.of. said branch. con duits}, a charge. of .a solid reducing.a'gentadapted it dammit-whims oxygen located in theheated portion. or the:other ema conduit, l means. 'for mg; the, thermal-conductivities ofgases in. wo, cells whereby the theoretical fuel-air jrfatio; isindicated by equal thermal-conductiyities bi'ltreatedggas ficwingto ther'espective cells a lean mixturev is indicated by a departure} ,fromtyijin .one direction, anda rich-mixture, is

other direction, independent of variations in the absolutethermalsconductivities of the exhaust gas when different fuels are used.

l8. ,A'p ar'atusior analyzing the .gas flowing in an e mangane econnected to .a .device,;in ch the combustion of air-"and lamhydrocarbon1 issues andlwhichpro duc'e's not; exhaust gases c'ofnpiising a mainexhaust conduit; connected "c'erssiea mg cit. hot. exhaust gases a seam.1 test cells, rseparate branch i bw i i t l -s l nes rom saidiiia'inexhaust conduit to 'sndrespecuve cells, portions of the respectivebranch conduits being located in heat exchange relationship with heatedexhaust gas flowing in said main exhaust conduit, a charge of copperoxide adapted to oxidize unburned fuel components located in the heatedportion of one of said branch conduits, a charge of a carbon adapted tocombine with free oxygen located in the heated portion of other branchconduit, means for comparing the thermal-conductivities of gases in saidtwo cells whereby the theoretical fuel-air ratio is indicated by equalthermal-conductivities of treated gas flowing to the respective cells, alean mixture is indicated by a departure from equality in one direction,and a rich mixture is indicated by a departure from equality in theother direction, independent of variations in the absolutethermal-conductivities of the exhaust gas when dilierent fuels are used.9. In the analysis by thermal-conductivity methods of the exhaust gasresulting from the combustion of air and a hydrocarbon fuel, whichexhaust gas has a minimum thermal-conductivity for the theoreticallycorrect fuel-air ratio, the steps which comprise treating the exhaustgas with a solid reducing agent to convert any free oxygen therein tocarbon dioxide whereby the treated exhaust gas possesses athermal-conductivity which increases as the fuel-air ratio increasesthrough a rang including 'both lean and rich mixtures, and measuring thedifference between the thermal-oonductivity of the treated exhaust gasand the thermal-conductivity of a reference gas sample. 10. In theanalysis of thermal-conductivity methods of the exhaust gas resultingfrom the combustion of air and a hydrocarbon fuel, which aeaaeze stepswhich comprise treating the exhaust gas with carbon to convert any freeoxygen therein to carbon dioxide whereby the treated exhaust gaspossesses a thermal-conductivity which'increases as the fuel-air ratioincreases through a range including both lean and rich mixtures, andmeasuring the difference between the thermalconductivity of the treatedexhaust gas and the thermal-conductivity of an auxiliary gas sample.

11. Apparatus for analyzing the exhaust gas resultin from the combustionof air and a hydrocarbon fuel in a combustion device, which exhaust gashas a minimum thermal-conductivity for the theoretically correctfuel-air ratio, a test cell, a conduit for delivering a stream of theexhaust gas to be tested to said cell, means including a charge of asolid reducing agent located in Said conduit to convert any free oxygenin the exhaust gas being supplied to said test cell into carbon dioxidewhereby the treated exhaust gas possesses a thermal-conductivity whichincreases as the fuel-air ratio increases through a range including bothlean and rich mixtures, and means connected to said test cell forindicating changes in the thermal-conductivity of treated exhaust gasdelivered thereto over said range of lean and rich mixtures.

12. Apparatus for analyzing the exhaust gas resulting from thecombustion of air and a hydrocarbon fuel in a combustion device, whichexhaust gas has a minimum thermal-conductivity for the theoreticallycorrect fuel-air ratio, a test cell, a conduit for delivering a streamof the exhaust gas to be tested to said cell, means including a chargeof carbon located in said conduit to convert any free oxygen in theexhaust gas being supplied to said test cell into carbon dioxide,whereby the treated exhaust gas possesses a thermal-conductivity whichincreases as the fuel-air ratio increases through a range including bothlean and rich mixtures, and means connected to said test cell forindicating changes in the thermal-conductivity of treated exhaust gasdelivered thereto over said range of lean and rich mixtures.

13. Thermal-conductivity gas analyzing apparatus comprising: a pair oftest cells; a metering system controlled by said test cells to indicatedifierences in thermal-conductivity of the gases in said two cells;separate conduits for delivering two separate streams of gas to saidrespective cells, one of said conduits including a charge of a solidoxidizing agent for normally oxidizing oxidizable components in the gasstream flowing therethrough to the associated cell, said oxidizing agentbeing restorable to oxidizing condition by treatment with oxygen; andmeans including a valve structure operable to admit gas from the otherconduit to both cells to calibrate said metering system and tosimultaneously flow oxygen to said oxidizing agent to restore it.

' WLADIMIR M. ZAIKOWSKY.

References Cited in the file of this patent UNITED STATES PATENTS NameDate Rodhe Mar. 17, 1925 Gerrish Oct. 13, 1942 Papers of the Bureau ofStandards, No. 249, part of vol. 18, Jan. 7, 1924, page 49.

Number

1. IN A METHOD OF DETERMINING THE RATIO OF A FUEL AND AIR MIXTURE BEINGSUPPLIED TO A COMBUSTION DEVICE, THE STEPS WHICH COMPRISE; FORMING AFIRST SRTEAM OF EXHAUST GAS EXHAUSTED FROM SAID DEVICE; TREATING SAIDFIRST STREAM OF EXHAUST GAS WITH AN OXIDIZING AGENT WHICH WILL ALTER THETHERMAL-CONDUCTIVITY OF SUCH EXHAUST GAS ONLY IF SAID MIXTURE IS RICH,THE TERMAL-CONDUCTIVITY OF SAID FIRST STREAM THEREBY DECREASING WITH THEFUEL-AIR RATIO; FORMING A SECOND STREAM OF EXHAUST GAS EXHAUSTED FROMSAID DEVICE; TREATING SAID SECOND SRTEAM OF EXHAUST GAS WITH A REDUCINGAGENT TOO ALTER THE THERMAL-CONDUCTIVITY OF SUCH EXHAUST GAS ONLY IFSAID MIXTURE IS LEAN, THE THERMAL-CONDUCTIIVITY OF SAID SECOND STREAMTHEREEBY INCREASING WITH THE FUEL-AIR RATIO; AND COMPARING THETHERMAL-CONDUCTIVITIES OF SAID TWO TREATED STREAMS; WHEREBY THEORETICALRATIO IS IN DICATED BY EQUAAL THERMAL-CONDUCTIVITIES OF THE STREAMS, ALEAN MIXTURE IS INDICATED BY A DEPARTURE FROM EQUALITY IN ONE DIRECTION,AND A RICH MIXTURE IS INDICATED BY A DEPARTURE FROM EQUALITY IN THEOTHER DIRECTION, INDEPENDENTLY OF VARIATIONS IN THE ABSOLUTETHERMAL-COONDUCTIVITIES OF THE EXHAUST GAS RESULTING FROM DIFFERENTFUELS.